NRES 201 Lecture 22 Outline of Last Lecture I Why is this topic important II Soil aeration Basic Concepts III Composition of soil air IV Oxidation reduction redox potential V What happens when a soil is waterlogged VI Factors affecting soil aeration and Eb Outline of Current Lecture VII Ecological effects of soil aeration VIII Managing soil aeration IX Wetlands and their soils Current Lecture Ecological effects of soil aeration Residue decomposition o Microbial activities depend on soil aeration o More rapid decomposition under aerobic conditions Because most soil microbes are active And there is a high level of metabolic efficiency o Much slower decomposition in poorly drained soils Because of fewer anaerobic microbes And much lower metabolic efficiency So organic matter accumulates Nutrient availability o Soil aeration controls the oxidation status of several elements o Water logging promotes reduction of Fe and Mn With higher plant availability in neutral or alkaline soils But toxicities can develop in acidic soils o Fe reduction can increase P availability Because Fe phosphates become more soluble Toxicities o Redox potential determines the solubility and mobility of Arsenic As Chromium Cr Selenium Se These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute o Soil drainage will reduce toxicity by As or Se By promoting oxidation o Organic matter additions will reduce Cr toxicity By promoting reduction and chelation Soil Color o Affected by the oxidation status of Fe and Mn o Well drained oxidized soils are red yellow and reddish brown o Poorly drained reduced soils are gray or grayish blue Greenhouse gas emission o Poor soil aeration promotes microbial production of Methane CH4 And Nitrous Oxide N2O o Like CO2 these gases absorb infrared radiation o Their atmospheric concentrations have increased markedly within the past century o Wetland soils are a major source Plant growth o Lack of O2 is the main problem for plant growth in flooded or saturated soils o Plants respond by closing leaf stomata which reduces Photosynthesis Sugar translocation Water and nutrient uptake Hormone activity o Symptoms include Wilting Nutrient deficiencies Death Managing Soil Aeration Container grown plants o Potting mixes formulated to minimize water logging and poor aeration As well as for nutrient supply o Soil based potting mixes mineral soil by volume Inert coarse grained materials promote drainage Perlite expanded volcanic glass Vermiculite expanded mica Pumice porous volcanic rock Coarse sand Wetlands and their soils What is a wetland o An ecosystem in transition between land and water o Distinguished by soils that are water saturated near the surface and become O2 depleted from plant and microbial growth No wetland o If the water is too deep for rooted vegetation to emerge or if the soil does not become O2 depleted Wetland hydrology o Water balance Inflow from Surface runoff Subsurface seepage Precipitation Outflow from Evaporation Transpiration o Hydro period Refers to the temporal pattern of water table changes Daily hydro period for coastal marshes Seasonal hydro period for inland swamps bogs or marshes
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